Engine starter drive



Dec. 13, 1932.

W. L. M GRATH ENGINE STARTER DRIVE- Filed March 1, 1932 INVENTOR BY wmm.mc rat/v M AK A ORNEY Patented Dec. 13, 1932 UNITED STATES PATENTOFFICE WILLIAM I. MCGRATH, F ELMIR A, NEW YORK, ASSIGIN'OR TO ECLIPSEMACHINE COMPANY, OF ELMIRA, NEW YORK, A. CORPORATION OF NEW YORK ENGINESTARTER DRIVE Application filed March 1, 1932. Serial No. 596,120.

This invention relates to engine starter drives and more particularly toa drive embodying a novel form of yielding driving connection and novelarrangements of the cooperating parts.

In commercial types of starter drive embodying a pinion threaded on ascrew shaft for engaging an engine gear, a yielding driving connectionfor the pinion is provided in the form of a coiled spring anchored atits ends to the screw shaft and the shaft of the starting motor.

It has been found to be important in drives of this character that theanchoring pins for the ends of the springs be protected so far aspossible from bending stresses resulting from the driving loads, andvarious expedients have been perfected for placing the pins undersubstantially pure shearing stresses during the driving operation inorder to avoid overloading the pins.

Moreover, in some installations of this character, the idle positions ofthe screw shaft and pinion are determined by the length of the drivespring, and the longitudinal yield of the screw shaft to enforce mesh ngis provided for by spacing the convolutions of the ing a coiled drivespring in which the spring is so formed as to transmit practically noth-511g but shear stresses to its anchoring pins.

Another object is to provide such a device embodying means forsupporting the spring and limiting its deflection under load, such meansbeing so formed as to avoid binding or the setting up of localizedstresses in the members of the drive.

A further object is to provide such a device in which the drive springmay be com- 0 paratively closely wound whereby its capacity may beincreased while its overall dimensions are reduced.

It is another object of the invention to provide such a device which isso arranged that the drive spring draws the screw shaft against a stopwhich determines its idle position, and the spring is arranged tostretch lengthwise during the operation of enforcing mesh between thepinion and flywheel gear.

Further objects and advantages will be apparent to those skilled in thisart from the following description taken in connection with theaccompanying drawing in which:

Fig. 1 is a side elevation partly in section of a preferred embodimentof the invention;

Fig. 2 is an end view on an enlarged scale of the drive spring thereof;and

'Fig. 3 is a side view of said spring.

Referring first to Fig. 1 of the drawing there is illustrated a drivingshaft 1 which may be the extended armature shaft of a starting motor,not shown. The free end of the shaft 1 is preferably journaled asindicated at 2 in a housing a portion of which is ing member in the formof a pinion 5 in position to be moved longitudinally into and out ofengagement with a member of the engine to be started such as theflywheel gear 6. The outer or idle position of the pinion 5 is definedby the heel 7 of the threads on the screw shaft 4. and the pinion isnormally retained in its idle position by suitable means such as ayielding detent 8 which is arranged to cooperate with an inclinedshoulder 9 on the screw shaft to form an anti-drift device for 16 and apin 17 which is arranged to traverse registering openings 18 and 19 insaid head and shaft respectively, but being too short to'bind againstthe shaft 1. The driven head 15 is also formed as a smooth cylinder ofthe same diameter as the driving head 11 and is counterbored asindicated at 21. to receive a reduced extension 22 of said driving headwhereby the two heads have a loose telescoping joint therebetween.

According to the present invention, a yielding driving connectionbetween the driving and driven heads is provided in the form of a coiledspring indicated generally at 23 having a cylindrical body portion 24and terminating in radial eyes 25 and 26 which are arranged to surroundsnugly the'pins 13 and 17 and to be gripped thereby firmlv to thedriving and driven heads respectively. The center distance between theeves 25 and 26 when the spring is free is made equal to or slightly lessthan the center distance between the pins 13 and 17 when the device isassembled whereby the spring-yieldably maintains the driving and drivenheads in abutting relation as shown, the two heads forming a smoothcylinder within the spring 23, the joint 27 therebetween being locatedsubstantially midway between the pins 13 and 17 and said cylinderforming means for limiting the winding up of the spring 23 due todriving loads transmitted therethrough.

According to the present invention, the spring 23 is so formed that thepins 13 and 17 are subjected to sub'tantially pure shearing stressesduring the driving operation. As here illustrated, this is accomplishedby form- 1 ing the portion of the ends of the spring adjacent theanchoring pins so as to bear snugly on the cylindrical surface of theheads for a substantial di-"tance whereby bending stresses on the pinsare prevented. As here illustrated, these inwardly displaced portions ofreduced radius are quadrantal or longer, and it has been found inpractice that these portions are preferably formed so that the springbears on the heads at points from 90 to 120 degrees removed from theanchoring pins. The quadrantal end portions 28 and 29 of the springs areconnected to the cylindrical body portion 24 thereof by sections 31 and32 of intermediate curvature. These sections are preferablysubstantially semi-circular in extent in order that the ends thereof mayproperly line up with the adjacent portions of the spring and thevarious portions will merge smoothly into each other.

' The cylindrical. body portion 24 of the spring is formed withsufiicient radius to allow the spring to wind up in performing itsyielding driving function. The cylinder formed by the members 11 and 15,however,

is adapted to support the convolutions of the spring and preventdistortion thereof beyond the elastic limit in case of abnormal stressapplied thereto.

' Referring particularly to Fig. 2 of the drawing,'the quadrantalterminal portion 29 is formed with a radius 1' equal to the radius ofthe heads 11 and 15, and extends through an are a which as illustratedis approxima ely 120 degrees from the axis of the eye 26. The bodyportion 24 of the spring is for-med with a radius t which issufliciently greater than the radius 1' to allow the proper space 33between the body of the spring and the surface of the cylindrical headsto permit the desired amount of winding up of the spring to take place.The body portion 24 of the'spring is connected to the quadrantal portion29 by means of the intermediate portion 32 which is formed approxi--mately with a radius 8 intermediate the radii 1' and t and offset fromthe axis of the drive by a distance 0 equal to one half the differencebetween the radii 1' and t. The intermediate portion 32 is formed toextend through the are 1) which as illustrated is substantially 180degrees whereby the ends of the portions 32 merge smoothly into the endsof the quadrantal portion 29 and the body portion 24.

It will be understood that the term quadrantal as used with reference tothe terminal portions of the springs is not intended to define an arc ofexactly 90, but is intended to include structures as illustrated whichvary considerably from precisely a quarter of a circle. It will also beunderstood that due to the large radial thickness of the springmaterial, and the stresses set up in winding the spring, theintermediate portion 32 may not be a true semi-circle, but the preciseshape of that portion is not important as long as it merges smoothlyinto the body and terminal portion of the spring, and the termssemicircle and radius are therefore not intend-.

ed to apply with geometric precision.

The eyes 25 and 26 of the spring are formed with the inner edges 34 and35 thereof curved on the radius 1' (Fig. 2) whereby they conform closelyto the surfaces of the heads 11 and 15. It will readily be appreciatedthat this close conformation of the terminal portions of the spring tothe cylindrical surfaces of the heads will prevent any rocking motion ofthe ends of the springs on the cylinders during driving and thus preventthe application of bending stresses to the anchoring pins. It has alsobeen found that drive springs embodying the invention have a much longerlife than drivesprings now in general use but without the endconvolutions of reduced radius.

The convolutions of the springs are preferably formed of greater radialthan axial thickness in order that the torque capacity of the spring maybe large compared with its resistance to extension, and thus largedriving loads may be carried without permanently distorting the spring,while the spring is comparatively limber with respect to tension appliedthereto.

lln the operation of the device, starting with the parts in thepositions illustrated in F ig. 1, rotation of the shaft 1 by thestarting motor in the direction of the arrow will cause the screw shaft4 to be rotated by reason of the connection through the driving head 11,spring 23 and driven head 15. The pinion 5, however, by reason of itsinertia, will not immediately assume the rotation of the screw shaft andwill therefore be traversed longitudinally into mesh with the enginegear 6. When the longitudinal motion of the pinion 5 is stopped bytheshoulder 36 on the driven head 15, the pinion is compelled to rotatewith the screw shaft whereby rotation is transmitted to the engine gearto crank the engine.

The loads transmitted through the spring 23 may cause the same to wrapdown on the heads 11 and 15, but since the joint 27 between said headsis located under the middle portion of the spring, this wrapping downdoes not cause a binding of the parts or set up localized stresses suchas might occur if the joint were near either end of the spring where itmight be gripped by the spring before the spring had been completelywrapped down to its limiting position. The spring 23 thus serves to forma suitable yielding driving connection for the cranking operation.

When the engine starts, the rotation of the engine gear 6 causes thepinion 5 to overrun the threaded shaft 4 whereby the pinion is traversedback to its normal position where it is retained by anti-drift means 8,9.

If, during the meshing movem'ent of the pinion 5, a tooth of the pinionshould abut end to end with a tooth of the engine gear 6, furthertraversal of the pinion is momentarily interrupted whereby the screwshaft 4 will out, as to yieldingly resist this endwise movement of thescrew shaft 4 whereby the frictional resistance between the threads onthe screw shaft and pinion is allowed to build up until it overcomes thefriction between the ends of the teeth on the pinion and engine gear.When this takes place, the pinion 5 is rotated by the screw shaft 4 intoproper indexed relation with the engine gear, whereupon the pinion isquickly drawn into meshing relation by the contraction of spring 23. Thecompletion of the meshing of the pinion and the cranking operation thentake place in the usual manner.

It will be seen that there is here provided a structure whereby theobjects of the invention are accomplished as above set forth, but itwill be understood that certain changes may be made in the details ofconstruction and arrangements of the parts without departing from thespirit of the invention as defined by the claims appended hereto. Itwill also be understood that although the invention is illustratedherein as applied to an inboard type of drive, it is equally applicableto the well known outboard type of drive.

What is claimed is:

1. In an engine starter drive, a rotatable shaft having a cylindricaldriving head thereon, a driven shaft having a cylindrical head normallyabutting and forming an extension of said driving head and yieldingdriving means for connecting said heads comprising a coiled springadapted to loosely surround the cylinder formed by the driving anddriven heads the end convolutions of the spring being displaced inwardlyand reduced in radius so as to bear on said heads a substantial distancefrom the ends of the springs.

2. In an engine starter drive, a rotatable shaft having a cylindricaldriving head thereon, a driven shaft having a cylindrical head normallyabutting and forming: an extension of said driving head and yieldingdriving means for connecting said heads comprising a cylindrical coiledspring adapted to loosely surround the cylinder formed by the drivingand driven heads, the end convolutions of the springs being displacedinwardly and reduced in radius so as to bear on said heads at least 90degrees from the ends of the spring.

3. In an engine starter drive, a rotatable shaft having a cylindricaldriving head thereon. a driven shaft having a cylindrical head normallyabutting and forming an extenion of said driving head, and yieldingdriving means for connecting said heads comprising a coiled springadapted to loosely surround the cylinder formed by the driving anddriven heads, the end convolutions of the spring being displacedinwardly and reduced in radius so as to bear on said heads a substantialdistance from the ends of the springs, said spring having substantiallysemi-circular portions of intermediate radius connecting the portions ofreduced radius with the main body of the spring.

4. In an engine starter drive, a-rotatable shaft having a cylindricaldriving head thereon, a driven shaft having a cylindrical head normallyabutting and forming an extension of said driving head and yieldingdriving means for connecting said heads comprising a coiled springadapted to loosely surround the cylinder formed by the driving anddriven heads with its ends anchored to said heads, the end convolutionsof the spring being displaced inwardly and reduced in radius so as tobear on said heads at least 90 degrees from the ends of the spring thejunction between the driving and driven heads being arrangedsubstantially midway between the anchorages for the ends of the spring.

5. In an engine starter drive, a coiled driving spring comprising acylindrical body portion, substantially quadrantal end portions ofreduced radius terminating in radial eyes, and substantiallysemi-circular portions of intermediate radius connecting the endportions to the cylindrical body portion.

6. In an engine starter drive, a coiled driving spring comprisingacylindrical body portion, substantially quadrantal end portions ofreduced radius terminating in radial eyes, and substantiallysemi-circular portions of intermediate radius connecting the endportions to the cylindrical body portion, the inner edges of said radialeyes being formed as continuations of the inner edges of said quadrantalend portions.

7. In an engine starterdrive, a coiled driving spring having itsconvolutions substantially thicker radially of the spring than axiallthereof, comprising a substantially cylind iical body portion,substantially quadrantal coaxial end portions of reduced radius, andsubstantially semi-circular portions of intermediate radius .connectingthe end portions to the body portion, said end portions terminating inradial eyes forming extensions of said quadrants.

8. Starting mechanism for internal combustion engines comprising adriving shaft having a cylindrical driving head fixed thereon, a drivenshaft Journaled on the driving,

a shaft having a cylindrical driven head fixed thereonand normallyabutting said driving head, said heads having portions adapted to have aloose telescop ng fit and forming together a smooth continuous cylinder,a member mounted on said driven shaft and connected thereto forlongitudinal movement thereon into and out of engagement with a memberof an engine to be started and rotation therewith to drive said enginemember, and a coiled drive spring anchored at its ends to said drivingand driven heads and with its body portion spaced from said heads.

9. Starting mechanism for internal combustion engines comprising adriving shaft having a cylindrical driving head fixed thereon, a drivenshaft journaled on the driving shaft having a cylindrical driven headfixed thereon and normally abutting said driving head, said heads havingportions adapted to have a loose telescoping fit and forming together asmooth continuous cylinder, a member mounted on said driven shaft andconnected thereto for longitudinal movement thereon into and out ofengagement with a member of an engine to be started and rotationtherewith to drive said engine member, and a coiled drive springanchored at its ends to said driving and driven heads. at pointssubstantiallv equally spaced axially from their joint line.

10. Starting mechanism for internal combustion engines comprising adriving shaft having a cylindrical driving head fixed thereon, a drivenshaft journaled on the driving shaft having a cylindrical driven headfixed thereon and normally abutting said driving head, said heads havingportions adapted to have a loose telescoping fit and forming together asmooth continuous cylinder, a member mounted on said driven shaft andconnected thereto for longitudinal movement thereon into and out ofengagement with a member of an engine to be started and rotationtherewith to drive said engine member, and a coiled drive springanchored at its ends to said driving and driven heads, at pointssubstantiallv equally spaced axially from their joint line, and arrangedto yieldingly maintain said ends in contact, said engine driving memberbeing arranged to approach said spring in its engaging movement, where-'by obstruction of such movement is yieldingly opposed by the tension ofsaid spring.

11. Starting mechanism for internal combustion engines comprising adriving shaft having a cylindrical driving head fixed thereon, a drivenshaft journaled on the driving shaft having a cylindrical driven headfixed thereon and normally abutting said driving head, said heads havingportions adapted to have a loose telescoping fit and forming together asmooth continuous cylinder, a member mounted on said driven shaft andconnected thereto for longitudinal movement thereon into and out ofengagement with/a member of an engine to be started and rotationtherewith to drive said engine member,

and a coiled drive spring anchored at its ends to said driving anddriven heads, at

points substantially equally spaced axially from their ioint line, theterminal quadrantal portions of said spring being arranged to conform tothe cylindrical heads whereby the spring anchorages are placed undersimple shear loads during the driving operation.

12. Starting mechanism for internal combustion engines including adriving shaft having a substantially cylindrical driving head fixedthereon, a driven shaft having a substantially cylindrical driven headfixed thereon and normally abutting said driving head, a member mountedon said driven shaft and connected thereto for longitudinal movementthereon into and out of engagementwith a member of an engine to bestarted, and for rotation therewith to drive said engine member, and acoiled driving spring anchored at its ends to said driving and drivenheads, the terminal portions of said spring being formed to bear on saidheads at points substantially spaced from their anchorages, and theintermediate portions of said spring being normally spaced radiallv fromsaid heads.

13. In an engine starter drive, a rotatable shaft having a driying headthereon,a driven shaft having a driven head thereon, said heads beingrelatively movable in an axial direction and being extended by axiallyoverlapping and relatively movable parts, and yielding driving means forconnecting said heads comprising a cylindrical coiled spring surroundingsaid parts and drivingly connected to said heads, the end convolutionsof the spring being displaced inwardly and reduced in radius so as tobear on said heads a substantial distance from the ends of the spring.

14. In an engine starter drive, a rotatable shaft having a driving headthereon, 'a driven shaft having a driven head thereon, said heads beingrelatively movable in an axial direction and being extended by axiallyoverlapping and relatively movable parts, and yielding driving means forconnecting said heads comprising a cylindrical coiled spring looselysurrounding said overlapping parts and drivingly connected to saidheads, the

end convolutions of the spring being displaced inwardly and'reduced inradius so as to bear on said heads at least from the ends of the spring.I v

15. In an engine starter drive, a rotatable shaft having a driving headthereon, a driven shaft having a driven head thereon, said heads beingrelatively movable in an axial direction and being extended by axiallyoverlapping and relatively movable parts, and yielding driving means forconnecting said heads comprising a cylindrical coiled spring surroundingsaid parts and drivingly connected to said heads, the end convolutionsof the spring being displaced inwardly and reduced in radius so as tobear on said heads a substantial distance from the ends of the spring,said spring having portions of inter mediate curvature connecting theportions of reduced radius with the main body of the spring and shapedso that contiguous portions of diiferent curvature merge with each othersmoothly and without abrupt changes in curvature.

16. -A coiled driving spring for engine starter drives comprising a mainbody portion having coils of equal radius, substantially quadrantal endportions of reduced radius, and portions of intermediate curvatureconnecting said end portions with the main body of the spring and shapedso that contiguous portions of different curvature merge with each othersmoothly and without abrupt changes incurvature.

In testimony whereof, I have hereunto signed my name.

WILLIAM L. MCGRATH.

